A wireless local area network (WLAN) basically supports a basic service set (BSS) mode including an access point (AP) serving as a connection point of a distribution system (DS) and a plurality of stations (STAs), however, not APs, or an independent BSS (IBSS) mode including only stations (STAB) (hereinafter, AP and STA will be referred to as a ‘terminal’).
In a wireless communication system using multiple antennas, MIMO system, a channel capacity is increased according to an increase in the number of antennas, and frequency efficiency can be enhanced accordingly. The MIMO system may be classified into the following two types of systems: a first one is a single user (SU)-MIMO, in which multiple streams are transmitted only to a single user, and a second one is a multi-user (MU)-MIMO in which multiple streams are transmitted to multiple users by canceling interference between users by an AR.
The MU-MIMO is advantageous in that it can obtain even a multi-user diversity gain along with the increase in channel capacity. Also, the MU-MIMO scheme can simultaneously transmit multiple streams to multiple users by using the same frequency band, increasing throughput in comparison to an existing communication scheme. In general, throughput of the wireless communication system can be increased by increasing the frequency band, but a system cost is disadvantageously increased according to the increase in the frequency band. Meanwhile, the MU-MIMO scheme does not increase the frequency band but its complexity is drastically increased in comparison to the existing communication scheme. Thus, in the standard such as 802.11ac, methods for simultaneously employing the MU-MIMO technique while using a variable frequency according to a surrounding situation have been researched.
In the wireless communication system in which multiple antenna streams are simultaneously transmitted to several users while using a variable frequency band, a data field and a signal field including information regarding the corresponding data field are transmitted. The signal field is divided into the following two types of fields. The first is a common signal field including information commonly applied to users. The second is a dedicated signal field including information individually applied to each user. The common signal field may be recognized by every user who belongs to a common user group or who may not belong to the common user group. Also, the common signal field is used for auto-detection for discriminating by which communication system a transmitted data frame has been generated (namely, it is used for auto-detection for discriminating a communication system by which a transmitted data frame was generated), so that, the common signal field is required to have compatibility. Thus, there is a limitation in changing the format or the configuration of the common signal field.
The common signal field is transmitted through a simple iterative structure to an SNR gain and a frequency diversity gain. However, the dedicated signal field cannot obtain both the SNR gain and the frequency diversity gain although such a simple iterative structure as that of the common signal field is used.